i get the logs at the start of the summer so they dry out, a cubic ton bag is around £35 probably double that for the ready to burn logs, other places such as home bargains you can pick up the pre dried logs around 3.99 a bag but thats going to be expensive, never realy worked the costing out TBH, i'd say 3 or 4 good logs will give me around 90 minutes burn time, so if i put it on say around 6pm when i get in i can burn 12 logs so about £1.50 a night, i source other stuff like waste timber etc and burn it with logs so this reduces the running cost even more, coal gives a better heat as it burns at a higher temp but not keen on using it as it smokes the fire glass, had it in over 7 years now and wouldnt be without it